1. Field
This invention relates to a retransmission method for a digital broadcast and its broadcast receiving device. More specifically, the present invention relates to, for example, a retransmission method for a digital broadcast and its receiving device which are capable of reducing a burden of an edge router in broadcasting an Internet protocol (IP) broadcast.
2. Description of the Related Art
In recent years, a so-called IP broadcast employing an IP multicast distribution technology has started in a communication network. The IP broadcast utilizes transmission information such as a multicast address to transmit broadcast signals. A receiver acquires the transmission information corresponding to a broadcast channel in advance and tunes a desired program by notifying a multicast address assigned to the desired program to an edge router on a transmission side via a higher order router to be connected. An Internet group management protocol (IGMP) is used for an IP v4, and a Multi Listener Discovery (MLD) is used for an IP v6 as protocols, respectively.
In the IP broadcast, a retransmission of a terrestrial digital broadcast will also be supposed in future years. A digital broadcast generally performs a multiplex transmission of channel tuning information and program-related information as a broadcast signal in a form of a Transport Stream (TS) defined by MPEG-2 systems together with a video/audio signal of a program. An encoding transmission system of the channel tuning information and the program-related information is defined by ARIB-STD B10 etc. and composed of a variety of types of information tables also referred to as Service Information (SI).
More specifically, the channel tuning information with the transmission frequency, etc., described therein is described in each table of a network information table (NIT), a broadcaster information table (BIT) and a service description table (SDT), and the event information is described in an event information table (EIT).
The receiver acquires these items of the information to utilize them to tune programs and to display program-related information such as an electronic program guide (EPG).
For the terrestrial digital broadcast, especially, each broadcasting station performs a multiplex transmission of only its own SI on its own broadcast signal. Therefore, the receiver sequentially channel-searches broadcasting channel frequencies capable of receiving within a service area, appropriately, for instance, after power supply of the receiver is turned on, to acquire and update the SI, such as the channel tuning information and the program-related information. In other words, the existence of a plurality of broadcasting stations that may be accessed within the service area makes the receiver scan the plurality of broadcasting channel frequencies to acquire the SI of each broadcast station. Here, it is defined that the search of an unknown channel is referred to as ‘channel search’ and the sequential changes in channel frequencies of known broadcasts are refereed to as ‘channel scan’.
Incidentally, for the retransmission of the terrestrial digital broadcast by the use of the system of the IP broadcast, a transmission of a description part on a transmission frequency, etc., of the NIT by replacing it to the description on the IP multicast address, etc., at a retransmission side, like a trans-modulation in a CATV head-end is a possible approach.
However, if a large number of receivers to which the broadcast signals are distributed intend to perform channel scanning in order to acquire and update the SI like an ordinary reception of the broadcast signals being on the air (broadcasted), frequent channel-change requests may occur to the edge router on the transmission side. The higher the number of the receivers to which the broadcast signals are distributed, the higher the treatment burden of the edge router is. And when the burden exceeds a processing capability, the whole distribution system probably fails.
To countermeasure the failure, for instance, Jpn. Pat. Appln. KOKAI Publishing No. 2005-38340 discloses a method for describing version numbers of other broadcasting stations in broadcast signals from each terrestrial broadcasting station to broadcast them by changing the SI transmission operation of the current terrestrial broadcast and for performing the multicast transmission of the SI by all stations via a communication network. However, it is not easy for this publicly-known example to change the current broadcasting operations from the aspect of interference on existing broadcast receiver and it is needed for each terrestrial broadcast station to modify facilities for both broadcast and communication, so that this publicly-known method is extremely hard to be realized.
According to one aspect of this invention, an object of the present invention is to provide a method and a device which is capable of performing the retransmission of the digital broadcast signals through the IP broadcast and capable of operating smoothly and simply on both transmission and reception sides without having to change the operations and facilities for the current terrestrial broadcast.